Sabot projectiles are used when an oversized gun tube launches an undersized warhead. These projectiles have sabot petals or segments wrapped around the warhead and contact the bore of the gun tube during ejection. The sabot seals the bore to prevent escape of the propulsion gases during firing and then drops away from the warhead when it leaves the gun tube. One such projectile is an armor piercing, fin stabilized discarding sabot which has three sections around a central core or body. These sections are held together with a front bourrelet and a band or obturator at the rear. A fin assembly stabilizes the central core in flight.
A worn gun tube has an enlarged bore that is eroded due to excessive firings. Thus, its diameter exceeds that of the sabot projectile. This causes balloting of the sabot petals due to misalignment and vibration which gives the projectile a tendancy to break up in the worn tube during launch.